Gerrit Jan van Ingen Schenau

Coordination in vertical jumping

The present study was designed to investigate for vertical jumping the relationships between muscle actions, movement pattern and jumping achievement. Ten skilled jumpers performed jumps with preparatory countermovement. Ground reaction forces and cinematographic data were recorded. In addition, myoelectric activity (EMG) was recorded from seven leg muscles. EMG-signals were rectified and low-pass filtered to obtain EMG-levels. The latter, which were assumed to reflect activation levels, rose to a plateau in the sequence m. semitendinosus, long head of m. biceps femoris, m. gluteus maximus, m. vastus medialis, m. rectus femoris, m. soleus, m. gastrocnemius. It was attempted to link the EMG-pattern to the purpose of the push-off, namely to maximize the effective energy (Ey) of the mass center of the body (MCB). The term Ey designates the sum of the potential energy of MCB and the kinetic energy due to the vertical velocity of MCB. One of the requirements for maximization of Ey is that the mono-articular extensor muscles release as much energy as possible before toe-off occurs. It is argued that this requirement can only be satisfied if the vertical velocity differences between the proximal and distal ends of body segments reach their peaks in a sequence. The sequence that is realized by the pattern of muscular activation is upper body, upper legs, lower legs, feet. Another important requirement is that the mechanical energy released by the muscles is optimally used. This requirement can be satisfied by transportation of energy via the biarticular m. rectus femoris and m. gastrocnemius.

Mechanical output from individual muscles during explosive leg extensions: The role of biarticular muscles

The main result of this study is that biarticular leg muscles contribute significantly to the work done at joints, due to transfer of power during explosive leg extensions. In particular, a net power transfer was shown from hip to knee joint during jumping and sprinting. Seven elite athletes performed explosive one legged jump and spring push offs. Kinematics, ground reaction forces and electromyography (EMG) of leg muscles were recorded. The mechanical output of six individual muscle groups was estimated by using Hill-based muscle models. The EMG and kinematics served as input to these models. For jumping as well as for sprinting, the model estimated similar results for the relative work contribution done about a joint due to transfer of power by the biarticular muscles. Rectus femoris showed a power transfer from hip to knee joint, while in contrast hamstrings showed a power transfer from knee to hip joint. Regardless of these opposite directions of power transfer, a net transfer occurred from the hip to the knee joint. The relative work contribution of hamstrings done in hip extension was 7% in jumping and 11% in sprinting. For rectus femoris, the relative work contribution done in knee extension was 21% in jumping and 31% in sprinting. Power transferring actions by gastrocnemius from knee to ankle contributed 25% in jumping and 28% in sprinting to the work done in plantar flexion. These results support the hypothesis that the action of biarticular muscles contributes to a net transfer of power from proximal to distal joints during explosive leg extensions. This action of the biarticular muscles causes an efficient conversion of body segment rotations into the desired translation of the body centre of gravity.

The influence of the biarticularity of the gastrocnemius muscle on vertical-jumping achievement

Hypotheses concerning the influence of changes in the design of the human musculoskeletal system on performance cannot be tested experimentally. Computer modelling and simulation provide a research methodology that does allow manipulation of the systems design. In the present study this methodology was used to test a recently formulated hypothesis concerning the role of the biarticularity of the gastrocnemius muscle (GAS) in vertical jumping [Bobbert and van Ingen Schenau, J. Biomechanics 21, 249-262 (1988)]. This was done by comparing maximal jump heights for a model equipped with biarticular GAS with a model equipped with a monoarticular GAS. It was found that jump height decreased by 10 mm when GAS was changed into a monoarticular muscle. Thus, the hypothesis formulated by Bobbert was substantiated, although quantitatively the effect is small. Our result differs from that of Pandy and Zajac [J. Biomechanics 24, 1-10 (1991)], who performed similar model calculations. It is shown that the results described by these authors can be explained from the moment-arm-joint-angle relation of GAS at the knee in their model.

Drop jumping. I. The influence of jumping technique on the biomechanics of jumping.

In the literature, drop jumping is advocated as an effective exercise for athletes who prepare themselves for explosive activities. When executing drop jumps, different jumping techniques can be used. In this study, the influence of jumping technique on the biomechanics of jumping is investigated. Ten subjects executed drop jumps from a height of 20 cm and counter-movement jumps. For the execution of the drop jumps, two different techniques were adopted. The first technique, referred to as bounce drop jump, required the subjects to reverse the downward velocity into an upward one as soon as possible after landing. The second technique, referred to as counter-movement drop jump, required them to do this more gradually by making a larger downward movement. During jumping, the subjects were filmed, ground reaction forces were registered, and electromyograms were recorded. The results of a biomechanical analysis show that moments and power output about knee and ankle joints reach larger values during the drop jumps than during counter-movement jumps. The largest values were attained during bounce drop jumps. Based on this finding, it was hypothesized that bounce drop jump is better suited than counter-movement drop jump for athletes who seek to improve the mechanical output of knee extensors and plantar flexors. Researchers are, therefore, advised to control jumping technique when investigating training effects of executing drop jumps.

Drop jumping. II. The influence of dropping height on the biomechanics of drop jumping

In the literature, athletes preparing for explosive activities are recommended to include drop jumping in their training programs. For the execution of drop jumps, different techniques and different dropping heights can be used. This study was designed to investigate for the performance of bounce drop jumps the influence of dropping height on the biomechanics of the jumps. Six subjects executed bounce drop jumps from heights of 20 cm (designated here as DJ20), 40 cm (designated here as DJ40), and 60 cm (designated here as DJ60). During jumping, they were filmed, and ground reaction forces were recorded. The results of a biomechanical analysis show no difference between DJ20 and DJ40 in mechanical output about the joints during the push-off phase. Peak values of moment and power output about the ankles during the push-off phase were found to be smaller in DJ60 than in DJ40 (DJ20 = DJ60). The amplitude of joint reaction forces increased with dropping height. During DJ60, the net joint reaction forces showed a sharp peak on the instant that the heels came down on the ground. Based on the results, researchers are advised to limit dropping height to 20 or 40 cm when investigating training effects of the execution of bounce drop jumps.

Intermuscular coordination in a sprint push-off

This study was designed to investigate the patterns of intermuscular coordination during a sprinting event. In previous research it was found that despite the indeterminacy problem of movement control, movements like vertical jumping, speed skating and cycling are performed in a stereotyped manner. It was hypothesized that this might be due to constraints associated with the transformation of joint rotations into the desired translation. The objective of the present study was to determine the extent to which the intermuscular coordination patterns during other movements also are performed in a stereotyped manner and, if that is true, whether this can be understood on the basis of such constraints. Seven elite sprint runners were instructed to execute an explosive sprinting dash. Ground reaction forces and cinematographic data were recorded for the second stance phase of the sprint. Simultaneously, electromyographic activity of nine leg muscles was recorded telemetrically. Linked-segment modeling was used to obtain net joint moments and net joint powers. Different athletes appeared to perform the sprint in a stereotyped manner. The muscle coordination pattern is characterized by a proximo to distal sequence in timing of the monoarticular muscles. When compared to the sequential pattern found in jumping, the biarticular hamstrings and rectus femoris muscles behave differently; in the sprint a more pronounced reciprocal activity between these muscles exists. The resulting movement pattern is characterized by a sequence of upper leg extension and plantar flexion. The observed sequence in timing of muscle activation patterns is aimed at solving the problems associated with the earlier identified geometrical and anatomical constraint. However, the coordination pattern cannot be fully understood on the basis of these constraints. A specific constraint is identified with respect to the direction of the ground reaction force, which explains the pronounced reciprocal activity of the biarticular hamstring and rectus femoris muscles. The intermuscular coordination pattern in the sprint can be seen as a compromise between the specific requirement of the sprint and the advantageous effect of a proximo to distal sequence as found previously for jumping.

Function of mono- and biarticular muscles in running.

In this study the function of leg muscles during stretch-shortening cycles in fast running (6 m.s-1) was investigated. For a single stance phase, kinematics, ground reaction forces, and EMG were recorded. First, rough estimates of muscle force, obtained by shifting the EMG curves +90 ms, were correlated with origin-to-insertion velocity (VOI). Second, active state and internal muscle behavior were estimated by using a muscle model that was applied for soleus and gastrocnemius. High correlations were found between estimates of muscle force and VOI time curves for mono-articular hip, knee, and ankle extensor muscles. The correlation coefficients for biarticular muscles were low. The model results showed that active state of gastrocnemius was high during increase of origin-to-insertion length (LOI), whereas active state of soleus was low during the start of increase of LOI and rose to a plateau at the time lengthening ended and shortening started. It seems that the difference in stimulation between gastrocnemius and soleus is a compromise between minimizing energy dissipation and using the stretch-shortening cycle optimally. Furthermore, it was found that the net plantar flexion moment during running reached a value of 302 Nm, which was 158% and 127% higher than the peak values reached in maximal jump and sprint push-offs, respectively. It was argued that the higher mechanical output in running than in jumping could be ascribed to the utilization of the stretch-shortening cycle in running. The higher values in running compared with sprinting, however, may lie in a difference in muscle stimulation.

Ice friction during speed skating

Abstract During speed skating, the external power output delivered by the athlete is predominantly used to overcome the air and ice frictional forces. Special skates were developed and used to measure the ice frictional forces during actual speed skating. The mean coefficients of friction for the straights and curves were, respectively, 0.0046 and 0.0059. The minimum value of the coefficient of ice friction was measured at an ice surface temperature of about −7°C. It was found that the coefficient of friction increases with increasing speed. In the literature, it is suggested that the relatively low friction in skating results from a thin film of liquid water on the ice surface. Theories about the presence of water between the rubbing surfaces are focused on the formation of water by pressure-melting, melting due to frictional heating and on the ‘liquid-like’ properties of the ice surface. From our measurements and calculations, it is concluded that the liquid-like surface properties of ice seem to be a reasonable explanation for the low friction during speed skating.

Isokinetic plantar flexion: experimental results and model calculations.

In isokinetic experiments on human subjects, conducted to determine moments that can be exerted about a joint at different angular velocities, joint rotation starts as soon as the moment increases above the resting level. This contraction history differs from the one in experiments on isolated muscle, where the force is allowed to increase to an isometric level before shortening is initiated. The purpose of the present study was to determine the influence of contraction history on plantar flexing moments found during maximal voluntary plantar flexion on an isokinetic dynamometer. In ten subjects, plantar flexing moments were measured as a function of ankle angle at different angular velocities. They were also calculated using a model of the muscle-tendon complex of the human triceps surae. The model incorporates elastic tendinous tissue in series with muscle fibers. The input of the model consists of time histories of active state (the force generating capacity of contractile elements) and shortening velocity of the muscle-tendon complex. Different time courses of active state were offered at fixed length of the muscle-tendon complex. The time course yielding a close match between the calculated rise of plantar flexing moment and the rise measured during fixed angle contractions was used to calculate moment-angle curves for isokinetic plantar flexion. The active state value reached when a peak occurred in calculated moment-angle curves was found to be lower if the angular velocity was made higher. Comparing measured and calculated results, it was concluded that moment-angular velocity diagrams determined in studies of isokinetic plantar flexion in human subjects reflect not only the influence of shortening velocity of contractile elements on the force which can be produced by plantar flexors.

Differential use and control of mono- and biarticular muscles

Abstract Most purposive movements are multi-joint actions in which specific patterns of joint moments are necessary to achieve the required segmental accelerations and to exert the appropriate direction and magnitude of force on the environment. Both human and animal studies suggest that mono- and biarticular muscles have different roles in these complex movements. Monoarticular muscles appear to show simple flexor or extensor activation patterns closely related to the required joint displacements, whereas biarticular muscles often exhibit complex multiple bursts of activity aimed at a fine-regulation of the distribution of net moments over the joints of the limb. Different patterns of activation of mono- and biarticular muscles have been observed during natural movements and in response to sudden perturbations or peripheral afferent inputs. Evidence is provided that the control of mono- and biarticular muscles is based on different processes and different sources of information. Monoarticular muscles may be more rigidly grouped into simple flexor or extensor synergies, whereas biarticular muscle activity may be more flexibly sculpted by motion-related feedback from peripheral afferents. Little is known about where and how the integration between perceptual information and the control of net joint moment is realized.